U.S. patent number 6,212,314 [Application Number 09/112,264] was granted by the patent office on 2001-04-03 for integrated opto-mechanical apparatus.
This patent grant is currently assigned to Lucent Technologies. Invention is credited to Joseph Earl Ford.
United States Patent |
6,212,314 |
Ford |
April 3, 2001 |
Integrated opto-mechanical apparatus
Abstract
A class of opto-electronic mechanical devices that include a
planar optical waveguide having a cladding in which there is
carried an evanescent electric field by a light beam traveling
along the waveguide and a mechanical micro-element controllably
coupled into the evanescent field for varying locally the
properties of the waveguide in a wavelength dependent fashion. The
devices described include optical switches and WDM add/drop
apparatus.
Inventors: |
Ford; Joseph Earl (Monmouth,
NJ) |
Assignee: |
Lucent Technologies (Murray
Hill, NJ)
|
Family
ID: |
22342979 |
Appl.
No.: |
09/112,264 |
Filed: |
July 8, 1998 |
Current U.S.
Class: |
385/30; 385/10;
385/37; 385/9 |
Current CPC
Class: |
G02B
6/12007 (20130101); G02B 6/29353 (20130101); G02B
6/3536 (20130101); G02B 6/266 (20130101); G02B
6/3548 (20130101); G02B 6/3584 (20130101); G02B
6/3596 (20130101); G02B 2006/12145 (20130101); G02B
2006/12159 (20130101) |
Current International
Class: |
G02B
6/12 (20060101); G02B 6/35 (20060101); G02B
6/34 (20060101); G02B 6/26 (20060101); G02B
006/26 () |
Field of
Search: |
;385/30,3,2,8,9,10,37,123 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
5854864 |
December 1998 |
Knoesen et al. |
|
Primary Examiner: Palmer; Phan T. H.
Claims
What is claimed is:
1. Apparatus comprising:
means providing an optical signal in a waveguide that is
characterized by a region surrounding the path of the light that
includes the evanescent field of the light;
MEMS means including a grating for affecting the optical signal
traveling along the waveguide; and
means for controllably inserting the affecting means in or out of
the region of the evanescent field of the optical signal traveling
along the waveguide, for affecting desired changes in the optical
signal in a wavelength dependent fashion.
2. Apparatus in accordance with claim 1 in which the affecting
means is a sequence of gratings, each reflective at a different
wavelength for affecting selectively power of said wavelength in
the optical signal.
3. Apparatus in accordance with claim 1 in which the providing
means provides a waveguide path that includes at least one input
port, at least two output ports, and an intermediate region
therebetween that includes a plurality of paths that are joined
together at their input and output ends, the input ends being
connected to at least one input port, and their output ends being
connected to the different output ports, and the means for
inserting inserts the light affecting means to a different degree
in the evanescent fields surrounding the plurality of paths whereby
an optical signal supplied to the input port of the waveguide may
be made to divide in a desired fashion between the output
ports.
4. Apparatus in accordance with claim 3 in which the affecting
means is a deformable MEMS element that includes separate portions
each overlying a separate one of the plurality of paths such that
each portion can be separately inserted into the evanescent field
of the optical signal in its adjacent path.
5. Apparatus in accordance with claim 1 in which the affecting
means is a rotatable grating positioned over the path of the
optical signal in its evanescent field, whereby the rotation of the
grating can be used to change, in a wavelength dependent manner,
the affecting properties of the grating.
6. Apparatus in accordance with claim 5 in which the rotation of
the grating can be used to remove wave energy of a selected
wavelength from forward travel in the wave path.
7. The method of affecting an optical signal traveling along a
waveguide that comprises positioning a MEMS that includes a
deformable control element including a grating adjacent the
waveguide, and
controllably deforming the deformable element in and out of the
evanescent field of the optical signal traveling along the
waveguide whereby the optical signal is affected in a wavelength
dependent fashion.
Description
FIELD OF THE INVENTION
This invention relates to opto-mechanical electronic devices, and
more particularly to a class of such devices that involves hybrid
integrated micro-optic mechanics.
BACKGROUND OF THE INVENTION
Integrated optics is a well-established technology using
lithography to define waveguiding paths on the surface of a planar
substrate to create a variety of passive and active components. As
used herein, passive components are those that route light without
detection and retransmission of data signals.
Passive integrated optics devices provide robust components for
power splitting, wavelength routing arid similar functions. Active
integrated optics devices typically use a refractive index change
from thermo- or electro-optic effects to switch light beams between
optical paths.
Optomechanical components potentially provide electro-mechanical
latching with no power dissipation. Micro-electro-mechanics is a
rapidly developing field that exploits lithographic mass
fabrication techniques to build miniature mechanical systems
ranging in size from millimeters to microns. As used herein, a
micromechanical element is a miniature element that has been shaped
by lithographic patterning followed by deposition of and/or etching
a workpiece, generally a multilayer structure of which several
layers typically are of polysilicon. Some of the polysilicon layers
are releasable by removal of intermediate sacrificial layers to
form mechanical structures. Such an element is then used in a
micro-electro-mechanical system (MEMS), for example in
micromechanical optics. MEMS devices are available from many
sources, as for example, the MEMS Technology Application Center at
North Carolina (MCNC). There is now an extensive body of literature
relating to such technology and its application to optical
switching. Typical of such literature is a paper entitled "MEM'S
the Word for Optical Beam Manipulation" published in Circuits and
Devices, July 1997, pp. 11-18.
It is normally difficult to combine the properties of
micro-mechanical optics and integrated optics in a single device
because of the incompatibility of their materials and in their
processing.
The present invention involves a new class of devices that are more
compatible to the combining of the two technologies of
micro-mechanical optics and integrated optics for use in hybrid
integrated micro-opto-mechanics (HIMOM).
SUMMARY OF THE INVENTION
The basic principle of a new class of devices that use hybrid
integrated micro-optics mechanics involves coupling to an optical
waveguide for affecting an optical signal traveling therein through
the evanescent electric field that accompanies the optical signal
in the surrounding waveguide cladding as the optical signal travels
along the waveguide. A basic advantage of a device that uses this
approach is that it allows micro-mechanical switching and routing
of the optical signal without the need for coupling the optical
signal out of the waveguide, thereby increasing the efficiency and
robustness of the resulting device, while lessening the need for
the compatibility of the materials used for switching or
waveguiding. Basically, this invention involves the movement of an
element, such as a membrane, of a MEMS controllably in and out of
the evanescent field of an optical signal traveling along a
waveguide to affect its travel along the waveguide. Since the
effect is stronger the closer the movable element is to the
waveguide, for maximum effect the element should get as close as is
feasible to the waveguide, typically as close as a fraction of a
micron.
For an optical signal of the kind presently used in optical
communication systems, the evanescent field does not extend in
significant strength beyond 0.1 and 0.5 microns from the waveguide.
This limited penetration into the space surrounding the waveguide
would make macro-mechanical techniques ineffective in using the
evanescent field for control purposes. Moreover, for maximum
effect, it is advantageous to thin, in the region of interaction,
the cladding that is normally used to cover the waveguide.
In a simple illustrative embodiment of the invention, a MEMS
membrane is positioned adjacent a waveguide and controllably
inserted in and out of the evanescent field of an optical signal
traveling along the waveguide for scattering the optical signal and
attenuating desirably further travel along the waveguide.
In another illustrative embodiment of the invention, a waveguide
interferometer switch, a section of a MEMS that is readily
deformable electromechanically is moved in, from out of, near
contact with a selected one of two arms of a Mach-Zender
interferometer so that then there is evanescent coupling by such
arm with the guided mode in the dielectric cladding surrounding the
waveguide. This coupling changes the effective index of refraction,
and therefore the optical length, of the affected arm. Such a
change affects the relative phase of the light waves in the two
arms and produces an unequal division of the power of the light
wave between the two output ports of the interferometer.
In another illustrative embodiment, a device that adds or drops
selectively a wavelength channel in a wavelength multiplex division
(WDM) system uses evanescent coupling to modify the reflective
properties of MEMS optical gratings to add or drop a channel of a
particular wavelength from a group of signal channels of different
wavelengths.
In some instances, the MEMS element may even serve to provide some
waveguiding.
The invention will be better understood from the following detailed
description taken in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
Each of FIGS. 1 through 5 depicts a different illustrative
embodiment of micro-electronic mechanic devices that use coupling
to the evanescent field surrounding a planar waveguide to control
light beams traveling in the waveguide.
DETAILED DESCRIPTION
FIG. 1 illustrates a particular arrangement 10 for attenuating
controllably an optical signal traveling along a planar waveguide
12 on a planar substrate 14. A MEMS in which there has been formed
a suspended deformable polysilicon portion of a MEMS, such as a
suspended membrane 16, is positioned over the waveguide 12. By
application of a force advantageously electrostatic, to deform the
membrane 16 in and out of the region of the evanescent field of the
signal traveling in a waveguide, the signal is scattered, thereby
attenuating it. The force can be provided by a voltage between the
membrane and the planar substrate 14 supporting the waveguide 12
since these typically are each of silicon. The attenuation can be
made sufficiently strong, if desired, essentially to cut off
further travel. Advantageously, the cladding (not shown separately)
normally covering the waveguide is thinned or removed in the region
of coupling to the membrane 16. Alternatively, there may be used a
segment of a higher index cladding to decrease the index
discontinuity and to confine the light wave tightly to the
waveguide to increase the sensitivity of the interaction.
FIG. 2 shows a Mach-Zender waveguide interferometer 20 that
comprises an input port waveguide section 21 and a pair of output
port waveguide sections 22A and 22B supported on a planar substrate
27. Between these waveguide sections is positioned a pair of
interferometer arms 23A, 23B of equal length that branch apart from
their junction 24 with the input port section 21 and join together
at junction 25 before branching into the output port sections 22A,
22B. A deformable element of a MEMS, such as membrane 26,
advantageously of the kind earlier described, is supported over the
interferometer arms at its opposite ends and at an intermediate
post 27. By deflecting electromechanically in any suitable
controllable fashion a selected one of the two halves of the
membrane 26 on either side of support port 16C into the region of
strong evanescent field of a light beam traveling along the
underlying arm of the interferometer, there is changed the relative
phase of the light waves in the separate arms. Accordingly, when
the two beams recombine at the output junction 25, because of
interference effects the relative difference in phase will result
in an uneven split of the combined light, as it exits via the
separate output ports 22A, 22B. Depending on the amount of the
relative phase shift introduced, almost complete transfer of the
light power to a selected one of the two output ports is feasible.
It can be seen that additional paths can be provided between the
junctions 24 and 25 and a MEMS element used to affect the optical
signal in such path in the manner described.
It is to be noted that this switching is effected without
interrupting the travel of the light beam in either arm from its
normal path or mechanically disturbing the waveguide paths, so that
the resultant device can be rugged and relatively lossless.
Moreover, both the MEMS including deformable member 26 and the
interferometer 20 can be fabricated independently on separate
substrates and later assembled together with little disturbance of
either.
FIG. 3 illustrates a HIMOM wavelength channel selectable add/drop
assembly 30 for use in a wavelength division multiplexing (WDM)
system. It includes a planar substrate 31 that supports a planar
waveguide 32 along which is traveling a multiwave-length optical
signal. Over the substrate 31 is positioned a MEMS 33 that includes
a sawtooth element that includes, by way of example, a pair of
relatively thick sawtooth grating sections 34A, 34B formed of a
polysilicon layer. Typically such a grating can be a surface
profile or index variation written by ultra violet light. These are
supported suitably over the waveguide 32 by posts shown but not
numbered. Each diffraction grating is controlled by a separate one
of conductive electrodes 35A, 35B in the MEM 33 so that either
grating can be moved in or out of the region of strong evanescent
field of the signal traveling in the waveguide 32. Advantageously,
to facilitate this the thickness of the waveguide cladding 38 is
reduced at regions 38A, 38B adjacent to the gratings. By
appropriate choice of the spacing of the grating teeth, each
grating 34A, 34B can be made to reflect selectively a particular
channel wavelength when the grating is moved into the evanescent
field at a region of thinned waveguide cladding. A sequence of
grating sections, each with different teeth spacing to be
reflective of a different wavelength, of which only two gratings
are shown in FIG. 3, can be spaced along the waveguide to reflect a
selected one of the multichannel wavelengths, as the appropriate
grating is moved into the evanescent field. The reflected light
going backwards can be selectively recovered in known fashion by
the use of an optical circulator, positioned to pass such reflected
light into a side port, while passing forward traveling beams to an
output port.
If preferred, it is possible to get the effect of a thick grating
from a sequence of relatively thin periodic structures provided the
segments of the periodic structure are appropriately spaced to
maintain coherence. For example, the selectivity of a 10 mm thick
grating can be achieved with 10 100-micron-thick segments placed at
900 micron intervals.
A grating could be added to the MEMS membrane 16 in the switch of
FIG. 1 to increase its scattering and switching action.
In FIG. 4 there is shown in top view apparatus 40 that includes a
MEMS that includes a grating structure 41 that can be used in an
analogous fashion to that shown in FIG. 3 as a WDM add/drop
assembly to reflect selectively a light beam of a chosen wavelength
from a multiwavelength beam. The grating structure 41 is positioned
over an intermediate section of the integrated optic waveguide 42
on substrate 44, and is rotatable. Its undersurface (not seen) is
provided with parallel lines of sawteeth to form a grating shown as
though they were on the upper surface that is seen in the figure.
Optical fiber couplers 45, 46 are provided at the opposite ends of
the planar waveguide 42 to serve as the input and output ports. The
rotatable member 41 is supported closely over the intermediate
section of the waveguide such that the sawteeth extend into the
evanescent field of the waveguide. The waveguide cladding, not
shown, is thinned in the region underlying the grating structure to
increase the evanescent field available. By rotating the grating 41
to vary the angle the lines of teeth form with the underlying
waveguide, there is varied the reflective effect of the grating.
For a thin waveguide structure, the rotated grating has an apparent
period that varies as the sign of the rotation angle. A tunable
add/drop effect results by rotating the grating to the appropriate
angle for the desired wavelength. If no reflection is desired, the
grating can be rotated to a position where the wave path is little
affected. Here again optical circulators adjacent at the input and
output ports can be used in standard fashion to divert
appropriately the added and/or dropped signals.
Alternatively, in the preceding arrangement the gratings can be
used to scatter selectively the light of a particular wavelength
whereby such light is effectively attenuated so that there is
formed a wavelength-dependent attenuator. As mentioned earlier, the
attenuation can be sufficiently large that light of the selected
wavelength is essentially eliminated from the traveling signal.
Hybrid integrated micro-optic-mechanics can be implemented with the
MEMS element and the waveguide structure either bonded together on
the same substrate. As shown in FIG. 5, a waveguide 51 is formed on
the underside of the planar surface of a suitable substrate 52,
such as a crystalline silicon or lithium niobate chip. In the
drawing, the waveguide extends essentially perpendicular to the
plane of the drawing. Then MEMS elements 53 are included, either
formed in layers, for example, of polysilicon deposited over the
original waveguide substrate, or as shown in FIG. 5 in a separate
planar silicon micromechanical substrate chip 56 that is bonded to
the original substrate waveguide chip, for example, by the
conventional flip-chip bonding technique used in silicon integrated
circuit technology. In this latter case, the spacing between the
two chips 52, 56 to have the MEMS element 53 positioned to affect
the evanescent field of a lightwave in the waveguide can be
controlled by the height of the solder bumps 57 used to bond
together the two chips. If desired, the spacing may be made closer
than the height of the solder bumps by recessing the bump sites.
Integrated optics chips are usually cleaved to obtain clean edge
surfaces, before being coupled to optical fibers. To simplify
fiber-to-waveguide alignment, it is now know to use etched silicon
substrates as templates. In analogous fashion, the micromechanical
substrate may be cleaved to provide fiber alignment features as
shown in FIG. 5 at 58 and 59. In a copending application filed on
Jun. 1, 1998 (Aksyuk et al. 10-2-17-18-16) and assigned to the same
assignee as the instant application, there are described hybrid
systems, in which a silicon chip including optical and/or
electronic elements is flip-chip bonded to a MEMS substrate.
It is also feasible to flip-chip bond entire wafers and then to saw
the bonded wavers into individual dice or chips. In such a case, it
would be advantageous to etch or score features into the separate
wafers before the bonding. However it may be difficult to saw a
chip that includes an integrated optics waveguide substrate.
However, by proper preparation and choice of the waveguide
substrate, it should be possible to cleave such a substrate without
damage to the waveguide by scoring appropriately the waveguide
optics substrate and then cleaving the bonded pair.
From the above examples, it should be apparent that HIMOM
technology has a versatility that adapts it for use in a variety of
devices that use mechanical elements to control opto-electronic
devices by close coupling to the evanescent field surrounding a
planar waveguide with no direct disturbance of the waveguide.
* * * * *